Radiology

Floron C. Faries, Jr. DVM, MS

Objectives

Determine the appropriate machine settings

for making a radiograph

Describe essential radiograph accessories

Describe the positions used to perform

radiographs from different views

Describe safety precautions and discuss their

importance

Terminology

X-ray tube of radiograph

machine

Vacuum tube

Cathode emits electrons

Anode collects electrons

Metal target on anode

Electron beam (electrical current) perpendicularly

directed X-rays (photons, radiation) emitted

Patient’s tissues absorb

Strike patient and redirect (scatter radiation)

High voltage power source

30-150 kilovolts (kV)

Milliamperage (mA)

Unit of measure

Controls amount of emitted x-rays

mA x exposure time (S) = mAs

Kilovoltage peak (kVp)

Value of voltage

Controls radiographic contrast of image

High mAs and low kVp = black and white image

Too high mAs = black image (over-exposed)

Too low kVp = white image (under-exposed)

Low mAs and high kVp = gray image

Source to image distance (SID)

Distance from anode to receptor (film, plate)

Increase distance = decreases beam intensity

Lightens images

Requires increasing mAs settings

Decrease distance = increases beam intensity

Darkens images

Requires reducing mAs settings

Reduces radiation exposure to patient

X-ray scatter control (reduces x-ray dose

exposure to patient and x-ray scatter)

Filtration device on x-ray tube

Filtration device of lead strips (x-ray grid)

Between anode and receptor (film, plate)

Requires increasing mAs settings

Requires increasing kVp setting for large animal thorax

Determination of Machine Settings

Measure thickness of patient’s part

Caliper instrument in centimeters

Use technique chart for thickness measurement

Position machine settings

kVp

mA

Exposure time

Set distance

Set needle of voltage line meter

1/16 inch above center line

Insures constant voltage coming into machine

Radiographic Positions

Head, neck, body, tail Dorsal – top view

Ventral – bottom view

Lateral – side view

Leg Anterior – front view

Posterior – back view

Lateral – outer side view

Medial – inner side view

Two views One plane

90º angle to first view

Imaging Modalities

Film/Screen Combinations

Cassette – holds film inside

Image produced on film – x-ray image (not visible)

Film development – image visible

Chemical, water, and drying times

Computer Radiology (CR) or Digital Radiography (DR)

Cassette – holds phosphor plate

Image produced on plate – x-ray image (not visible)

Plate development – image visible

Plate in reader – laser reads and digitizes into digital image

Digital image – sent to computer for viewing and storing

Plate erased and refreshed for reuse – by exposure to light

Computerized Axial Tomography (CAT) or Computerized Tomography (CT) Scan Utilizes x-rays

Produces cross-sectional images of soft tissue and bone

Ultrasonography (Ultrasound) Utilizes sound waves

Produces images (sonograms) of soft tissues

Motion images

Still images

Magnetic Resonance Imaging (MRI) Scan Utilizes radio waves

Produces images in any plane of body

Images and Tissue Density

Black image – air

Gray image – soft tissue

White image – bone, minerals, sand, metal,

dental enamel

Patient Motion

Voluntary motion (controlled motion) – restraint necessary Looking around

Moving away

Moving extremeties

Paddling

Pushing away

Involuntary motion (uncontrolled motion) – reduce exposure time, increase mA Heart beating

Breathing

Panting

Discomfort moving

Heart, lungs, and thorax images

Animal inhales – make exposure

Abdomen, pelvis, and spine images

Animal exhales – make exposure

Safety Devices and Precautions

Remove anyone from the x-ray room that is not needed.

Every person should wear a lead apron and lead gloves when holding the x-rayed animal.

Check the condition of gloves and aprons periodically by using radiography to determine if they allow x-rays to pass through.

Limit the beam to the size of the film with a cone or lead diaphragm.

Do not direct the x-ray beam into another room or work area.

Install an aluminum filter (1 to 2 mm thick) at the tube housing opening to eliminate radiation from useless wave lengths.

Cover the bottom side of the x-ray table with lead to protect the feet.

The hands should not be placed in the path of the direct beam.

Do not use fluoroscopy when radiography will do the job. Fluoroscopy is more hazardous and requires additional safety precautions.

Lead Gloves and Aprons

To help prevent deterioration of lead gloves

and lead aprons:

Roll or drape apron over curved surface rather

than folding it.

Store gloves by hanging or by placing cans with

both ends open inside gloves to keep the gloves

open and to allow moisture to evaporate.